Coating composition comprising paraffin wax, microcrystalline wax and petroleum distillate oil



COATING COMPOSITION COMPRISING PARAFFIN WAX, MICROCRYSTALLINE WAX ANDPETRO- LEUM DISTILLATE OIL No Drawing. Application July 16, 1957 SerialNo. 672,120

K i 2 Claims. c1. 208-21) This invention relates to a novel waxcomposition. More particularly, the invention relates to a novelcomposition containing a major proportion of a specific parafiin wax andminor proportions of a specific microcrystalline wax and a specificdistillate oil, the composition being especially suitable for coatingfibrous sheets and containers for packaging.

United States Patent Number 2,624,501 describes and claims a parafiinwax having specific properties which is especially suitable for coatingfibrous sheet materials and containers such as milk containers. Theclaimed paraffin wax has a melting point of from 125 F. to 132 F. and atensile strength at 40 F. of from 275 p.s.i. to 325 p.s.i. (pounds persquare inch), the tensile strength at 40 F. being at least 25 p.s.i.higher than the tensile strength at 70 F. An advantage stated for thiswax is that it is unnecessary to compound therewith foreign materials inorder to obtain good coatings with the wax. Actual commercial use,however, disclosed certain disadvantages of coatings formed from thiswax. Such coatings on fibrous sheet materials may develop minuteimperfections which impart a serpentine effect to the coating therebycreating an unsightly appearance, and leakage of packaged liquidmaterials through'the imperfections may develop. Another disadvantage ofthe wax is that it must be packaged for shipment in small lots toprevent blocking of the slabs of wax, i.e., to prevent fusion of stackedwax slabs into a large, single mass, especially when the stacked waxslabs are exposed to mildly elevated temperatures, such as temperaturesfrom about 80 F. to 90 F.

United States patent application Serial Number 504,- 366, filed April27, 1955, by John D. Tench, a coinventor of the present invention isdirected to a wax composition which overcomes the serpentine effect, andwax slabs prepared from the described composition do not block onstacking. These advantageous results are obtained by incorporating about2% by weight of a specific microcrystalline wax in the paraffin wax ofsaid United States Patent Number 2,624,501. While the described waxcomposition is good for many applications, such as for coating milkcontainers for packaging milk at 40 F., commercial use has disclosedthat it suffers from certain difiiculties. The primary diflicultyobserved with the wax composition is that coatings thereof on packagingmaterials crack when contacted with relatively cold materials, such asmilk at a temperature of 36 F. For example, milk containers coated withthis wax composition, when filled with milk at a temperature of 36 F.,exhibit cracking of the wax coating. Cracking is distinguished from theserpentine effect in that cracking is an actual break in the wax coatingwhich almost always results in leakage of the container.

An object of the present invention is to provide a Wax compositionespecially suitable for coating fibrous sheet materials such as fluidcontainers. Another object is to provide a wax composition havingsubstantially the properties of the paraflin wax described in UnitedUnited States Patent "ice States Patent Number 2,624,501, which whenapplied as a coating on fibrous materials, does not develop cracks whencontacted with a cold, fluid material. A further object is to providewax compositions which do not develop imperfections such as theserpentine effect. A still further object is to provide a waxcomposition which, when formed into wax slabs, does not block onstacking.

It has now been found that by incorporating small, critical amounts of aspecific microcrystalline wax and of a specific petroleum distillate oilin the parafiin wax of said Patent No. 2,624,501, the properties of theresulting wax composition are substantially the same as those of theparafiin wax, but the resulting wax composition does not crack ordevelop a serpentine effect when used as a coating on fibrous materials,and wax slabs formed from the wax composition do not block when theslabs are in stacked relationship.

It is essential to the successful preparation of the composition of theinvention that the microcrystalline wax have specific properties whichare described in said Serial Number 504,366. The microcrystalline waxmust have a melting point of from 185 F. to 200 F. (ASTM D127-49), aviscosity of from 81 to 89 SUS at 210 F. (D446-53), a refractive index(n of 1.435 to 1.438, a penetration of from 30 to 65 at 160 F. (ASTM D5-52), and a penetration of not above 5 at 77 F. (ASTM D552). Themolecular weight of the microcrystalline wax is approximately 650. Amicrocrystalline wax which does not have properties within the statedranges does not give a satisfactory wax composition when incorporated inthe paraffin wax of Patent No. 2,624,501.

The microcrystalline wax of the invention is prepared from petroleum.Slack wax from the dewaxing of lubricating oil is subjected to vacuumdistillation and the material boiling below about 490 F., and preferablybelow 525 F., at 2 mm. of mercury pressure is separated. The residualfraction is used to prepare the microcrystalline wax of the present waxcomposition. The residual fraction is dissolved in a solvent, such as amixture of methyl ethyl ketone and benzene, at an elevated temperature.The wax solution is then cooled to a temperature of from about 95 F. to110 F. and the wax precipitated at this temperature separated such as byfiltering. The resulting wax is the microcrystalline wax used inpreparing the present composition. It will be understood that othersolvents such as ethylene dichloride,

' toluene, and the like, may be employed for the dissoluseparated, suchas by filtering or centrifuging. The re-' tion of the wax at an elevatedtemperature. Substitution of such materials in whole or in part for thebenzene and/ or the methyl ethyl ketone may require an adjustment of thetemperature of precipitation, it being necessary that the final waxproduct have the properties as herein described. microcrystalline 'waxseparated such as by' filtering is advantageously washed with anadditional quantity of solvent, preferably used at the temperature ofthe precipitation, and that any excessive solvent is removed.

from the wax cake by means such as evaporation.

The preparation of the paraifin wax constituent of the present waxcompositions is advantageously accomplished as described by Patent No.2,624,501. Briefly, a slack wax obtained as a by-product from thedewaxing of lubricating oils, and which contains about 30% oil, issubjected to vacuum distillation and a distillate fraction boilingbetween about 325 F. and 650 F. at 10 mm. of mercury pressure isseparated. This fraction is dissolved in a solvent, preferably a mixtureof methyl ethyl ketone and benzene in about equal volumes, dissolutionbeing at a temperature of from about 165 F. to 195 F. The solution isslowly cooled to a temperature of from F. to F., and the precipitatedwax It will also be understood that the sulting filtrate is furthercooled to a temperature of from 25 F. to 30 F., and the precipitated waxfiltered. This latter filtered wax, on further treatment, forms theparaffin wax component of the wax composition of the present invention.It is preferred to wash the wax cake, either by washing the filter cakeor by repulping and subsequent filtration, using as the washing materialthe solvent employed in the dissolution of the wax. Also, the washingoperation is preferably conducted at a temperature approximating thetemperature of the final precipitation.

It is essential to the preparation of the composition of the inventionthat the petroleum distillate oil employed in the subject compositionhave specific properties. The oil must have an API gravity at 60 F. offrom 27.5 to 33, a viscosity at 100 F. of 100 to 650 SUS (SayboltUniversal seconds) and a pour point of F. maximum. Preferably a solventrefined petroleum distillate oil having the foregoing properties isemployed. The zero pour point limitation is necessary in order toprevent the introduction of relatively soft waxes or soft, waxlikematerials which, if present, would deleteriously affect the propertiesof the present composition.

It is essential that the concentration of the three components of thesubject wax composition be within certain limits. The paralfin waxcomponent must be present within the range of 95.5% to 96.7%. Themicrocrystalline wax must be present within the range of from 3% to 4%.The distillate oil must be present within the range of from 0.3% to0.5%. All quantities are herein expressed as percent by weight unlessotherwise designated. It will be noted that the quantity ofmicrocrystalline Wax is substantially above that shown to be operable inthe compositions of United States Serial Number 504,366.

The incorporation of the microcrystalline wax and paraffin wax can be byany convenient means, such as by blending the waxes in the mloten state,together with the oil, to obtain a homogeneous blend.

The following examples illustrate the compositions of the invention anddemonstrate the criticality of the concentration of the severalcomponents. In the examples, a dish test is used to demonstrate thesuitability or nonsuitability of wax compositions for coatingcontainers, such as milk containers. In accordance with this test, adefinite amount of the wax composition being tested is introduced into aglass petri dish and is placed in an oven maintained at a specifiedtemperature for a specified minimum time. Thereafter, the dish is cooledat a constant temperature for minutes and then immersed in cold waterfor 20 seconds. The dish containing the wax coating is then visuallyinspected and rated. In performing the dish test, the wax composition isheated to about 200 F. and 1010.1 grams introduced into at least twopetri dishes. The petri dishes are of Pyrex and have an outside diameterof 100 mm. The dishes are then placed in an oven maintained at 200 F. to210 F. for at least 15 minutes. The dishes are then removed from theoven and are cooled at 74i-4 F. for 30 minutes. During cooling thebottom of the dish should rest on an insulating material such asasbestos. The dishes and wax are then completely immersed in water at atemperature of 36i0.5 F. for 20 seconds. On removal from the water, thewax coatings are visually examined for cracking. On the rating scales,zero denotes no cracking, and 4 denotes severe cracking. A zero+ ratingis used to indicate very slight cracking. A composition which exhibits arating of 1 or above does not pass the test. The microcrystalline waxemployed in the examples was prepared by vacuum distilling slack waxfrom the dewaxing of lubricating oil to remove the components thereofboiling below about 525 F. at 2 mm. of mercury pressure. The residualfraction was dissolved in a solvent, consisting of a mixture of methylethyl ketone in about equal parts, at an elevated temperature. Theresulting solution was then cooled to a temperature of about 105 F. andthe wax precipitated at this temperature separated by filtration. Thewax cake was washed with additional solvent and solvent removed from thewashed cake by evaporation.

The resul'tins microcrystalline wax had a melting point of about 192 F.,a viscosity of about 86 SUS at 210 F., a penetration of about 47 at 160F. and about 3 at 77 F., a refractive index (11 of about 1.4363, and amolecular weight of about 650.

The parafiin wax was prepared as described in Patent Number 2,624,501,and had a melting point of about 127 F., a tensile strength of about 250at 70 F. and of about 280 at F.

The oil employed was a distillate solvent refined oil having an APIgravity F.) of from 31 to 33, a viscosity at F. of about SUS and a pourpoint of 0 F. maximum. The compositions of the examples were prepared bymelting the paraffin wax and blending therewith a microcrystalline waxand/or the distillate oil.

In preparing the compositions of the examples, the described componentsare blended at a temperature above the melting points of the waxesemployed so that, on cooling, a homogeneous blend is obtained.

Example 1 Paraffin (percent) Composition Oil (percent) Only compositions8 and 9, which illustrate compositions according to the invention,passed the dish test.

Example 2 A composition containing 9% paraffin wax, 3.5%microcrystalline wax and 0.5% oil, each of said materials having theproperties as above described, was prepared and used to coat a cardboardmilk carton. The coated milk carton was filled with milk at 36 F. Nocracking of the wax coating or leaking of the container was observed.

Another composition was prepared by blending 98% of the parafiin waxwith 2% of the microcrystalline wax. The resulting composition was usedto coat a cardboard milk container. On filling the coated container withmilk at 36 F., cracks developed in the wax coating covering the bottomof the container and severe leakage of the milk through the carton wasobserved.

When compositions containing more than 4% of the microcrystalline waxare used, the wax coating is uneven and furrowed, and hence suchcompositions are unsuitable for coating milk containers in that customerresistance is experienced and leakage, especially at the furrows, maydevelop. Also, when the compositions containing more than 05% oil areused, blocking is observed even at relatively low temperatures, e.g., atabout 70 F., and hence such compositions are unsuitable in accordancewith the present invention.

Example 3 The properties of a composition containing 96.7% paraflin wax,3% microcrystalline wax and 0.3% distillate oil is compared to theproperties of the paralfin wax alone in the following table:

Paratfin Wax- Wax Composition Melting point (ASTM D8742) 1 127 128Viscosity at 210 F. (ASTM D446-53) 39. 39.2 Refractive Index (m1.4218 1. 4222 Penetration (ASTM D 5-52):

at 77 F 20 15 at 100 F 105 85 Flash (F.) (ASTM D92-52) 430 420 carbonparaflin wax derived from petroleum and having a melting point of 125 F.to 132 F., a tensile strength at F. of from 275 to 325 p.s.i., thetensile strength at 40 F. being at least 25 p.s.i. higher than thetensile strength at F., from about 3% to 4% by weight of amicrocrystalline wax derived from petroleum and having a melting pointof from 185 F. to 200 F., a viscosity of from 81 to 89 SUS at 210 F., apenetration of from 30 to 65 at 160 F., and a penetration of not above 5at 77 F., and from about 0.3 to 0.5% by weight of a petroleum distillateoil having an API gravity at 60 F. of from 27.5 to 33, a viscosity at F.of from 100 to 650 SUS and a pour point of 0 F. maximum.

2. Wax composition according to claim 1 wherein said distillate oil is asolvent refined distillate oil.

References Cited in the file of this patent UNITED STATES PATENTS2,361,582 Adams et al. Oct. 31, 1944 2,624,501 Ferris Jan. 6, 19532,744,031 Mumma May 1, 1956 2,773,812 Tench Dec. 11, 1956 2,783,161Padgett Feb. 26, 1957 2,816,845 Capell et a1. Dec. 7, 1957

1. A WAX COMPOSITION CONSISTING ESSENTIALLY OF A HYDRO-CARBON PARAFFINWAX DERIVED FROM PETROLEUM AND HAVING A MELTING POINT OF 125 F TO 132F., A TENSILE STRENGTH AT 40* F. OF FROM 275 TO 325 P.S.I.., THE TENSILESTRENGTH AT 40* F. BEING AT LEAST 25 P.S.I. HIGHER THAN THE TENSILESTENGTH AT 70* F., FROM ABOUT 3% TO 4% BY WEIGHT OF A MICROCRYSTALLINEWAX DERIVED FROM PETROLEUM AND HAV-NG ING A MELTING POINT OF FROM 185*F. TO 200* F., A VISCOSITY OF FROM 81 TO 89 SUS AT 210* F., APENETRATION OF FROM 30 TO 65 AT 160* F., AND A PENETRATION OF NOT ABOVE5 AT 7M* F., AND FROM ABOUT 0.3 TO 0.5% BY WEIGHTT OF A PETROLEUMDISTILLATE OIL HAVING AN API GRAVITY AT 6O F OF FROM
 27. 5 TO 33.AVISCOSITY AT 1OO F. OF FROM 1OO TO 65O SUS AND A POUR POINT OF O F.MAXIMUM.